The present invention relates to an electromagnetic fuel metering and atomizing valve for a supply device on an internal combustion engine, for the purpose of supplying the said device with given quantities of finely atomized fuel for the formation of an air and fuel mixture.
Valves of the aforementioned type usually comprise a substantially cylindrical body housing an annular electromagnet coaxial with the same; a nozzle having a fuel supply hole and fitted on to the front end of and coaxial with the said body; and a plugging member sliding axially inside the said body and the said nozzle. The plugging member presents an active surface designed to cooperate with a seat formed on the nozzle, for closing the said supply hole, and guide surfaces on the nozzle, for guiding the plugging member during axial displacement of the same. The valve body presents a coaxial core designed to exert electromagnetic force on a keeper integral with the plugging member, for the purpose of controlling displacement of the same. Such force is generated subsequent to activation of the electromagnet inside the body, which presents a cylindrical side wall, a top wall connected to the core, and a bottom wall in which is formed a hole through which the plugging member slides, so as to form, for the magnetic flow generated by the said magnet, a substantially closed magnetic circuit comprising the said walls, the said core and the said keeper.
Valves of the type outlined briefly above present a number of drawbacks, which tend to be aggravated during operation, to the extend that the valve becomes totally unusable.
Firstly, sealing between the said active surface on the plugging member and the mating seat formed on the nozzle may be faulty, due to poor mating of the said surface and seat caused by the plugging member and nozzle not being perfectly coaxial. Secondly, atomizing of the fuel (which is performed mainly by the outer surface of a pin projecting from the bottom end of the plugging member, and by the surface of the said supply hole) is not entirely regular, due to imperfect roundness of the annular supply opening defined between the pin and the hole. This drawback, too, is a result of imperfect concentricity of the plugging member and nozzle. Finally, metering action (which is also performed by the said pin and hole surfaces) may differ from one injection cycle to another, and fail to conform strictly with required performance. All the above drawbacks are the result of imperfect concentricity of the plugging member and nozzle, which occurs both with the valve closed and, more especially, during displacement of the plugging member in relation to the nozzle. Perfect concentricity of the plugging member and nozzle under all valve operating conditions has been found to be unachievable, even using highly accurate, efficient guide means for guiding the plugging member in relation to the nozzle. Such guide means usually consist of two sets of guide surfaces spaced along the plugging member and designed to mate, with very little radial slack, with the inner surface of the nozzle. Even if the said slack is barely sufficient for enabling smooth axial slide of the plugging member in relation to the nozzle, concentricity between the said two components still remains less than perfect, due to the components, of the electromagnetic force generated by the electromagnet, perpendicular to the axis of the plugging member. Owing to inevitable machining and assembly errors, the resultant of the electromagnetic forces which acts on the plugging member, instead of being strictly axial, presents transverse components, which tend to throw the plugging member off-center, and give rise to reactions in the guide areas between the plugging member and the nozzle. The said reactions, in turn, result in severe wear on the guide surfaces of the plugging member, thus resulting in even greater off-centering and, therefore, an increase in the off-balancing components of the electromagnetic force. Off-centering of the plugging member and nozzle therefore tends to increase rapidly and considerably, due to the off-balancing transverse components responsible for the said wear also increasing considerably alongside increasing wear.